The Cytometry and Antibody Technology (CAT) Facility serves the University of Chicago Comprehensive Cancer Center (UCCCC) membership by providing all of the tools necessary to measure properties of cells and their products. The Fitch Monoclonal Subcore (FMS) develops the reagents used to label the cells, whereas the Flow Cytometry Subcore (FCS) provides the technology and staff expertise to use these reagents for experimental measurements. During the past 35 years, antibodies have become reliable and necessary tools in the continuously growing interdisciplinary approach to basic and clinical research, as well as the diagnosis, and treatment of disease. Antibody technology and its usage have evolved concurrently with flow and image cytometry and has become the dominant tool for the identification and classification of cells and cellular products, especially in the areas of cancer research. The Facility is utilized by UCCCC investigators in many areas of study involved in the basic and translational research of cellular phenotype and function. The specific aim of the CAT Facility is to provide instrumentation and antibodies for the analytical detection of subcellular components and proteins using a range of fluorescence and non-fluorescence-based detection technologies. Further, the CAT Facility is designed to meet the wide-spread needs for specialized cytometric analysis and continues to respond to the demand for new and improved technology. Among these improvements include an expanding Antibody/Hybridoma Bank that provides commonly used, highest quality purified antibodies, pre-titered conjugated antibodies for flow cytometry, and hybridoma lines to UCCCC investigators. Cytometric technology improvements include the latest in high-speed cell sorting, multi-laser analyzers for performing polychromatic flow cytometry. Image-based cytometers, and bead-based analyte detectors.